The disclosure of the following priority application is incorporated herein by reference:
Japanese Patent Application No. 11-299331 filed on Oct. 21, 1999.
1. Field of the Invention
The present invention relates to an exposure method and an exposure apparatus used in a photolithography process for manufacturing micro devices such as semiconductor circuits, image pick-up devices (such as CCDs), liquid crystal displays, plasma displays, and thin film magnetic heads.
2. Description of the Related Art
In a photolithography process for forming a fine pattern of an electric device such as a semiconductor circuit or liquid crystal display, a projection exposure apparatus such as a stepper is used when transferring an original pattern of a reticle as a mask onto a wafer (or a glass plate) as a substrate to be exposed. In such a projection exposure apparatus, to improve its resolution to address a still finer integration level of micro devices, its exposure wavelength has shifted to a still shorter wavelength region. As the exposure wavelength, 248 nm of a KrF excimer laser is mainly used at present, but a shorter wavelength of about 200 nm or less in the vacuum ultraviolet region has also come to be used. In other words, the 193 nm wavelength of an ArF excimer laser is now virtually in practical use, and a projection exposure apparatus utilizing a laser such an F1 laser (of 157 nm wavelength) or an Ar2 laser (of 126 nm wavelength), each having a still shorter wavelength, as an exposure light source is now being developed.
Further, since the resolution can be improved by increasing the numerical aperture (NA) of a projection optical system, a still larger NA of a projection optical system is also being developed. In this connection, because a smaller exposure view field (exposure field) of a projection optical system advantageously affects in realizing a larger NA, the view field of a projection optical system itself is made smaller on one hand and, on the other hand, scanning exposure type exposure apparatuses such as a step-and-scan type exposure apparatus, which secures virtually a large view field by relatively scanning a reticle and a wafer during exposure, are also under practical use.
In a scanning exposure type exposure apparatus, in particular, because each of stages, on which a reticle or a wafer is mounted, should be driven with high precision, an air bearing system, which reduces friction during the movement of the stage by floating the stage by airflow, is adopted as a supporting system for the stage.
In recent years, light of vacuum ultraviolet range has been proposed to be used as exposure light; however, optical materials having practically applicable transmittance relative to vacuum ultraviolet light and usable as a lens or a reticle are limited to synthetic quartz, quartz doped with, e.g., fluorine, and crystals such as fluorite (CaF2), magnesium fluoride (MgF2), and lithium fluoride (LiF). Further, vacuum ultraviolet light is strongly absorbed by gases on the optical path such as an oxygen gas, moisture, and a hydrocarbonaceous gas (hereinafter, called xe2x80x9cabsorbent gasxe2x80x9d), and, furthermore, evaporated organic substances and the like, which react with vacuum ultraviolet light and result clouding substances on the surface of an optical element, can also be regarded as absorbent gases. Therefore, to exclude those absorbent gases from the optical path of exposure light, the gases on the optical path are required to be replaced with gases such as a nitrogen gas or a rare gas having small absorbency relative to vacuum ultraviolet light (hereinafter, called xe2x80x9ctransmitting gasxe2x80x9d). For instance, with respect to oxygen concentrations, the average concentration should be controlled to a level of ppm order. When the residual concentrations of the absorbent gases does not satisfy such specifications, exposure energy on a wafer considerably decreases, and, as a result, the throughput deteriorates because a longer exposure time is required.
Meanwhile, since in an exposure apparatus, wafers are sequentially exchanged and transferred with a fine pattern, wafers are required to be frequently moved in and out (exchanged) between an inside space including an exposure path and an outside space where the wafers are conveyed. As a result, during the wafer exchange operation, absorbent gases such as an oxygen gas and moisture flow into the inside space along with the conveyed wafers, and easily evaporable organic substances and the like adsorbed on the wafers are also conveyed. Further, because photoresist coated on the wafers itself releases a hydrocarbonaceous gas and the like (outgases), the concentrations of absorbent gases in the optical path cannot be easily kept within a predetermined level with respect to the atmosphere in the vicinity of the wafers.
Also, with respect to an exposure apparatus utilizing vacuum ultraviolet light as its exposure light, when a conventional air bearing system is adopted as a supporting system of a wafer stage and a reticle stage, a large amount of gas is necessary to float the stages. As a result, the gas for floating may flow into the atmospheres, where the stages are positioned, in the vicinity of a wafer and a reticle. If the gas for floating is an absorbent gas as normal atmospheric air, the transmittance of the atmosphere decreases. It is therefore preferable that also as the gas for floating, highly-purified transmitting gas is used. However, there is a problem that, to continuously control the concentrations of absorbent gases in the gas for floating used in relatively high volume within a predetermined level, the associated running costs increase.
Further, with respect to a wafer stage and a reticle stage of an exposure apparatus, their positions are normally measured with high precision by means of laser interferometers. In a laser interferometer, a moving mirror and a fixed mirror are each illuminated with a laser beam, and the position of the moving mirror (movable stage) is measured with reference to the fixed mirror. Also with this case, to improve the measurement accuracy of the laser interferometer, it is preferable, while supplying a transmitting gas on the optical path of exposure light, that the influence of gas fluctuation, accompanying the transmitting gas supply, on the optical path of the laser beams is made as little as possible.
In view of the above, it is a first object of the present invention to provide an exposure method and an exposure apparatus by which, even when using vacuum ultraviolet light as exposure light, a high exposure light intensity can be obtained by controlling the decrease of transmittance on an optical path.
Further, it is a second object of the present invention to provide an exposure method and an exposure apparatus by which, when adopting an air bearing system as a supporting system of a stage that moves a reticle or a wafer and even when using vacuum ultraviolet light as exposure light, the decrease of transmittance on an optical path can be controlled without increasing operating costs so much.
Further, it is a third object of the present invention to provide an exposure method and an exposure apparatus by which, when measuring, by a laser interferometer, the position of a stage that moves a reticle or a wafer and even when using vacuum ultraviolet light as exposure light, the decrease of transmittance relative to exposure light can be controlled without decreasing the measurement accuracy of the laser interferometer.
Further, it is a fourth object of the present invention to provide an exposure method and an exposure apparatus by which, even in such a case where vacuum ultraviolet light is used as exposure light, the position of a reticle or a wafer can be accurately detected.
Also, it is another object of the present invention to provide a device manufacturing method capable of mass-producing devices with high throughput using such exposure methods above.
A first exposure method according to the present invention is an exposure method in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure method comprising: dividing the space between the projection system and the second object into a first space on the side of the projection system and a second space on the side of the second object and providing, in the boundary portion between the first and second spaces, an aperture portion at a region through which at least the exposure beam passes; and supplying a first gas that transmits the exposure beam to the first space side, wherein the first gas"" contamination degree of impurities that absorb the exposure beam is smaller than that of a second gas of the second space side.
In connection with the present invention, the kind of affecting impurities varies depending upon the wavelength of the exposure beam. Further, the transmittance of the space in the vicinity of the second object is apt to change due to impurities"" intrusion during the exchange of the second object and due to impurities and the like adhered to the second object itself. In contrast, in the present invention, because the space in the vicinity of the second object is divided into a first space and a second space, with the first space being supplied with a gas with high transmittance, the proportion, in the space in the vicinity of the second object, of the space with low transmittance relative to the exposure beam is made small, and thus the decrease of transmittance as a whole can be controlled. As a result, with the intensity of the exposure beam on the second object being maintained to be high, the throughput of the exposure process improves.
In this case, it is preferable that the first gas is blown in a single direction in the first space. As a result, the decrease of transmittance of the first space is controlled, and, at the same time, because with the gas condition of the space over the second object being stabilized, the refractive index distribution in the planes perpendicular to the optical axis is uniformed, and the imaging characteristics are also stabilized. Further, impurities such as an outgas and the like generating from the second object are also efficiently exhausted by the first gas.
Next, a second exposure method according to the present invention is an exposure method in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure method comprising: disposing a stage holding the first object or the second object and moving on a base member in a space supplied with a third gas that transmits the exposure beam; floating the stage on the base member in a differential exhaust system by blowing a fourth gas and sucking the fourth gas; and setting, at the same time, the permissible absorbency limits of the fourth gas relative to the exposure beam higher than that of the third gas.
According to the present invention above, because the stage is floated in a differential exhaust system, the leakage amount of the fourth gas to the outside is small. Accordingly, even when setting the absorbency limits of the fourth gas relative to the exposure beam high and thus decreasing the operating costs, the decrease of transmittance of the exposure beam on the optical path in the vicinity of the stage can be controlled.
Further, a third exposure method according to the present invention is an exposure method in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure method comprising: measuring the position of the first object or the second object relative to a predetermined reference member by illuminating a stage moving with the first object or the second object and the reference member with a measurement beam and a reference beam, respectively; and making both of the optical paths of the measurement beam and the reference beam to be gaseous atmospheres each having about the same contamination degree of impurities that absorb the exposure beam.
According to the present invention above, because while supplying a gas that transmits the exposure beam on the optical path of the exposure beam in the vicinity of the stage, both of the refractive index fluctuations of the gases supplied to the optical paths of the measurement beam and the reference beam are made to be about the same amount, the measurement accuracy is maintained high.
Further, a fourth exposure method according to the present invention is an exposure method in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure method comprising: dividing the space between the projection system and the second object into a first space on the side of the projection system and a second space on the side of the second object and providing, within the boundary portion between the first and second spaces, an aperture portion at a region through which at least the exposure beam passes; blowing a gas that transmits the exposure light to the first space; and exhausting, via the gas blown in the first space, a substance generated from the second object by the illumination thereof with the exposure beam from the optical path of the exposure beam.
According to the present invention above, because impurities such as an outgas and the like generating from the second object during exposure are efficiently exhausted by the first gas, the transmittance of the exposure beam is maintained high. Furthermore, because clouding substances generated by chemical reaction of the outgas substance are prevented from adhering to the forefront lens of the projection system (the lens nearest to the second object), the transmittance of the exposure beam is maintained high at all times.
Further, a fifth exposure method according to the present invention is an exposure method in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure method comprising: dividing the space between the projection system and the second object into a first space on the side of the projection system and a second space on the side of the second object and providing, within the boundary portion between the first and second spaces, an aperture at a region through which a detection beam for detecting the position of the first object or the second object passes; and supplying a gas through which the exposure beam passes to the first space.
According to the present invention above, the gas that transmits the exposure beam can be effectively supplied to the first space on the side of the projection system, and at the same time, the second object can be illuminated with the detection beam via the aperture.
Further, a sixth exposure method according to the present invention is an exposure method in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure method comprising: dividing the space between the projection system and the second object into a first space on the side of the projection system and a second space on the side of the second object; and setting the contamination degree of impurities of the first space smaller than that of the second space. According to the present invention, as with the first exposure method, the operating costs can be controlled to be low, and the transmittance of the exposure beam can be maintained high.
Next, a first exposure apparatus according to the present invention is an exposure apparatus in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure apparatus comprising: an aperture plate which is disposed between the projection system and the second object and on which an aperture for making the exposure beam pass through is formed; a gas supply mechanism that supplies a first gas that transmits the exposure beam to a first space between the aperture plate and the projection system; and an environment control mechanism that controls the environment of a second gas which is supplied to a second space between the aperture plate and the second object and transmits the exposure beam and, at the same time, of which contamination degree of impurities that absorb the exposure beam is different from that of the first gas.
Further, a second exposure apparatus according to the present invention is an exposure apparatus in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure apparatus comprising: a stage that holds the first object or the second object and moves on a base member; a chamber that substantially hermetically seals a space enclosing the stage; a gas supply device that supplies a third gas that transmits the exposure beam into the chamber; and an air bearing device that float the stage on the base member in a differential exhaust system by blowing a fourth gas and sucking the fourth gas, wherein the permissible absorbency limits of the fourth gas relative to the exposure beam is set higher than that of the third gas.
Further, a third exposure apparatus according to the present invention is an exposure apparatus in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure apparatus comprising: a stage that moves with the first object or the second object; a reference member that is stationary relative to the projection system; an interferometer that measures the position of the first object or the second object relative to the reference member by illuminating the stage and the reference member with a measurement beam and a reference beam, respectively; and a gas supply device that supplies each of gases each having about the same contamination degree of impurities that absorb the exposure beam to each of the optical paths of the measurement beam and the reference beam.
Further, a fourth exposure apparatus according to the present invention is an exposure apparatus in which a second object is exposed, via a projection system, with an exposure beam that has passed a pattern of a first object, the exposure apparatus comprising: an aperture plate which is disposed between the projection system and the second object and on which an aperture for making a detection beam for detecting the position of the first object or the second object pass through is formed; and a first gas supply mechanism that supplies a first gas that transmits the exposure beam to a first space between the aperture plate and the projection system.
Each of above exposure methods according to the present invention can be performed by the use of each of such exposure apparatuses.
It is to be noted that as the first, second, and third gases in the present invention, a nitrogen gas, a rare gas (helium, neon, argon, krypton, xenon, or radon), a mixed gas of these gases may be utilized. Furthermore, as the first, second, and third gases, the same gas with each other or different gases from one another may be utilized. On the other hand, in contrast with the first, second, and third gases, because the fourth gas is a gas for floating the stage on the base member, a gas, such as dry air, that has low transmittance relative to exposure light but is inexpensive can utilized as the fourth gas.
Further, the aperture plate in the present invention may be so configured that a through hole is formed as the aperture or that the through hole is provided with a glass substrate that transmits the exposure beam. Still further, the aperture plate may be constructed from a combination of a plurality of plates. In this case, the portion between the plurality of plates corresponds to the aperture.
Next, a device manufacturing method according to the present invention includes a process that transfers a device pattern onto a workpiece using an exposure method according to the present invention.
In accordance with to the above-described first, fourth, and sixth exposure methods according to the present invention, by locally supplying a gas that transmits the exposure beam to, for example, the first space on the side of the projection system, an outgas including impurities generating from the second object, for example, can be effectively excluded from the optical path of the exposure light. Thus, with the transmittance relative to the exposure beam being made high, the exposure intensity can be made high, and at the same time, the consumption of the gas can be made small, and thus the operating costs can be decreased. Further, this also effectively influences on the increase in longevity of the projection system.
Further, by making the shape of the aperture of the boundary portion between the first and second spaces, for example, a narrow slit-like form, the compatibility with a focus detection device of oblique incident type is facilitated, and thus the compatibility with precision focusing can also be facilitated.
Further, in accordance with to the second exposure method according to the present invention, by making an air bearing mechanism used, for example, in a scanning exposure type exposure apparatus to be a differential exhaust system, even when the specifications of the impurities gases (gases that absorb the exposure beam) in the gas for floating to be supplied to air pads are relaxed to a large extent, the transmittance of the exposure beam can be maintained high. Furthermore, the operating costs required for gas purification can be decreased.
Further, in accordance with to the third exposure method according to the present invention, by blowing gases that include substantially the same amount of impurities to both of the measurement side optical path and the reference side optical path of the interferometer for position measurement, measurement errors due to impurities on the optical paths of the interferometer can be decreased.
Further, in accordance with to the fifth exposure method according to the present invention, because the exposure intensity can be maintained high, and, at the same time, the second object can be illuminated with the detection beam via the aperture of the aperture plate, the position of the second object can be detected with high precision, and thus the image of the pattern of the first object can be transferred onto the second object with high resolution.
Further, the exposure methods according to the present invention can be performed by each of the exposure apparatuses according to the present invention, and, at the same time, in accordance with the device manufacturing method according to the present invention, because the intensity of the exposure beam can be maintained high, the throughput of manufacturing processes of various kinds of devices can be increased.